Video comprises a series of still images (i.e., “frames”) which, when played in sequence and at an appropriate speed, mimic real-life motion. Video may be encoded according to various standards. For example, video encoded according to the National Television System Committee (NTSC) standard has approximately 30 frames per second of video, each frame comprising approximately 480 horizontal lines of visual information.
Video may be progressive or interlaced. Progressive video displays all of the lines of a frame at the same time. Interlaced video comprises two fields per frame, or approximately 60 fields per second when using the NTSC standard. Each frame therefore comprises two fields, a first field having half of the horizontal lines of the frame (e.g., the even lines of the frame), and a second field having the other half of the horizontal lines of the frame (e.g., the odd lines of the frame). A field is drawn in its entirety occupying every other line of the frame followed later in time by the other field that is drawn on the other lines.
Flicker is an undesirable artifact that may be caused by frames displayed on interlaced output devices. Flicker may appear to a viewer as flashing or moving lines and may be more prevalent when certain types of video are displayed. For example, flicker may be more noticeable when a video contains thin lines or small high-contrast features. Flicker may also be noticeable in video sequences containing rotation and scaling. Flicker can be distracting and can be uncomfortable for many viewers.
Thus, what is needed is an anti-flicker filter without the limitations of conventional techniques.